The present invention relates to a method as set forth in the preamble of the appended claim 1 for connecting data flows in wireless communication according to the Internet protocol, a system as set forth in the preamble of the appended claim 6, and an access point as set forth in the preamble of the appended claim 8.
The International Standardisation Organisation ISO has developed an open system interconnection (OSI) model for describing the distribution of data transmission in different layers. The layers are, listed from top downwards, an application layer (layer 7), a presentation layer (layer 6), a session layer (layer 5), a transport layer (layer 4), a network layer (layer 3), a data link layer (layer 2), and a physical layer (layer 1). In view of the present specification, the most essential layers are the physical layer, the data link layer, the network layer, and the application layer.
The term xe2x80x9cInternetxe2x80x9d is commonly used to describe an information resource from which information can be retrieved from a data processor, such as a personal computer (PC). The data processor communicates via a modem with a telecommunication network. This information resource is distributed world-wide, comprising several storage locations which also communicate with the telecommunication network. The Internet is made operable by defining certain data communication standards and protocols, such as TCP (transmission control protocol), UPD (user datagram protocol), and IP (Internet protocol), which are used for controlling data transmission between numerous parts of the Internet. The TPC and the UDP are involved with preventing and correcting data transmission errors in the data transmitted in the Internet; the IP is involved with data structure and routing. The currently used versions of the Internet protocol are IPv4 and IPv6.
Thanks to the growing popularity of open data systems, the Transmission Control Protocol/Internet Protocol (TCP/IP) communication protocol has become a generally used protocol whereby computers of different sizes and brands can communicate with each other. TCP/IP support is currently available for almost all operating systems. The network layer protocol of TCP/IP, the Internet Protocol IP, is intended to be routed by gateways, i.e. routers. The routing is conducted by means of IP addresses and routing tables.
In the Internet, each device has its own individual IP address. In the Internet protocol version IPv4, the IP address consists of 32 bits, i.e. it is a digit of four bytes which is divided in two parts: an organisation-specific network address and a network-specific device address. In the more recent Internet protocol version IPv6, the length of address fields has been added to 128 bits, which means in practice that an individual address can be reserved for all devices that are connected with the Internet network. FIG. 1 shows in IPv6 the blocks of the data packet in Internet messages.
The header block consists of the following elements:
Version IP version of 4 bits (=6),
Prio. priority of 4 bits,
Flow label 24 bit label for identifying the connection in the application layer,
Payload length 16 bit integer indicating the length of the payload, i.e. the length of the packet after the header in bytes,
Next header data of 8 bits determining the header immediately following the IPv6 header,
Hop limit integer counter of 8 bits which is reduced by one at the each device (node) which transmits the packet further; the packet is rejected if the value is reduced to zero,
Source address the 128 bit address of the sender of the original packet,
Destination address the 128 bit address of the intended recipient.
The header is followed by the payload block, i.e. the actual information to be transmitted.
Physically, the Internet consists of communication networks arranged in a hierarchy, for example local area networks (LAN), regional telecommunication networks and international telecommunication networks. These communication networks are coupled internally and externally with routers which transmit information from the transmitting terminal equipment or from the preceding router in the chain of data transmission, and route the information to the receiving terminal equipment or to the next router in the chain of data transmission.
Below in this specification, the transmitting terminal equipment and receiving terminal equipment will also be called by the common term Internet host. The Internet hosts can be typically used either as the source host SH and the destination host DH. In the present specification, the Internet hosts connected in a wireless manner with the Internet network are called a wireless terminal.
An Internet host, coupled to the Internet network via a local area network LAN, is either provided with a permanently defined Internet address or the address is a dynamic address generated by the server of the local area network (for example by using a dynamic host configuration protocol DHCP). In case the Internet host is coupled by a modem to a telecommunication network, the telecommunication terminal must ask for an Internet address from an Internet service provider to which the Internet host is registered. This is conducted e.g. according to a point-to-point protocol (PPP) formed above the Internet protocol layer. In both cases, the information to be transmitted in the Internet is routed to the Internet host possibly via several communication networks and routers from a remote host by using a determined Internet address.
The IP defines the transmission of the communication in packets (datagrams). The packet data transmission is one reason for the popularity of the Internet, because it allows transmission in bursts which does not require constant on-line connection and makes it possible that several Internet hosts are coupled in the same telephone connection. When a router receives a packet containing a destination address, the router routes the packet forward, if there is free capacity in the buffer memory of the router and at least one open telephone line. If there is not sufficiently memory space or no open telephone line available at the moment, the packet is rejected and the source host or the preceding router must try retransmission later. In general, the Internet does not support time-critical data transmission, and the method of best effort offered by the Internet protocol is sufficient.
In the transmission of packets according to the Internet protocol, the packets can be transmitted directly to the receiver only when the network elements of the addresses of both the host and the destination are the same. In other cases, the packets are transmitted to a router which takes care of transmitting the packets further, either to the next router or to the destination, if the recipient is in the network of the router. In each router, each packet entering the router is transferred from the data link layer according to the OSI model to the network layer, where the header of the packets is examined, and on the basis of the address data therein, a decision is made where the packet is to be transmitted. For transmission, the packets are transferred back to packets of the data link layer. The packets running the same path constitute a so-called communication stream. Because the Internet protocol has the character of a connectionless protocol, the above-mentioned operations must be conducted for each packet entering the router. If the communication layer is fast, for example in accordance with the asynchronous transfer mode ATM, the processing of the packets takes a significant part of the time used for transmission. Thus, the whole transmission capacity of the transfer line cannot be utilised effectively. For correcting this situation, e.g. Internet Engineering Task Force (IETF) has developed a solution in which an attempt is made to accelerate the routing of communication streams. In this solution, which is called Layer 3/Layer 2 switching (L3/L2 switching) or Multi Protocol Label Switching (MPLS), an attempt is made to switch the communication flows in the router directly on the data link layer, thereby reducing the need for performing time consuming routing on the basis of the address data of the network layer.
In an MPLS switching solution, so-called MPLS domains are formed. When a packet arrives to the router of such an MPLS domain, routing is conducted on the network layer. In this context, a short label of fixed length is added to the packet. Packets provided with such a label can be switched in the router by utilising the routing table of the data link layer, thereby avoiding the routing of the network layer. The label is used as an index in the table which determines the switching to the next router to be carried out in the router. Thus, in the MPLS domain, the routing of the network layer is thus conducted at the stage when the packet comes to the domain and, in a corresponding manner, when the packet leaves the domain. In contrast, it is possible to conduct a faster switching inside the domain in the data link layer. However, this solution requires that in each router of the MPLS domain, also a network layer protocol is implemented at least partially, as well as Internet protocol stack. In the MPLS domain, there are always three routers participating in the switching: the router that has transmitted the packet, the router switching the packet, and the next router receiving the packet. Because the routers are normally permanent, also the switching table can be made permanent and be updated in situations when new routers are added or routers in use are removed.
Telecommunication networks and the Internet are two significant world-wide communication networks, and wireless telecommunication terminals are being developed for coupling therewith and for their use. For example, cellular networks make it possible to couple a wireless telecommunication terminal to a telecommunication network and offer a high quality of service with circuit-switched technology. These cellular networks and other mobile communication networks can be utilised also for coupling to the Internet network and for utilising multimedia services. However, the circuit-switched system has the disadvantage that the connection from a wireless telecommunication terminal to a wireless communication network is turned on during the whole connection, which takes up the capacity of the wireless communication network and limits the number of simultaneous connections.
Data transmission in packet form improves the degree of capacity utilisation of the communication channel in general, not only for retrieving information from the Internet. For example, packet data transmission can be used in applications, such as voice calls, video negotiations and other communications according to different standards. However, some of these applications are time-critical. For example in a real-time voice call, the service of best effort offered by the Internet protocol may cause significant delays in the transmission and transfer of the audio signal, which affects the understanding of the received audio signal so that e.g. speech is almost or totally unintelligible. Moreover, the delay (the time consumed from the transmission to the receipt of the packet) may vary during the transmission of the audio signal, depending on e.g. the load of the communication network and variations in transmission errors. The same applies also to the transmission of a video signal in real time. There may also be situations where the users of the Internet do not want as long delays as occur in many cases for obtaining information from the Internet.
In radio links, data is typically transmitted in a channel which is a certain frequency range. Within one system, several channels can be available simultaneously. Further, in full duplex data transmission, there are separate transmitting and receiving channels, whereby for example a base station transmits on the transmitting channel to the terminal device and the terminal device transmits on the receiving channel to the base station. A problem with radio links is that the radio channel is a limited resource which limits e.g. the band width and/or number of channels that can be reserved as well as the data transmission rate available for the radio link. The radio channel is liable to disturbances, such as distortion of the received signal caused by multi-channel propagation which is due to the fact that the same signal is received at the destination through different routes at different times. To reduce the effect of disturbances, part of the data transmission capacity must be used for transmitting error connection data with the packets, and achieving a desired error probability rate may require several packet retransmissions, which reduces the capacity of the radio link.
In radio links, where several data transmission flows are transmitted on one channel, packets of these different data transmission flows are multiplexed. The transmission order can be affected by arranging packets of different data transmission flows in an order of priority, whereby packets of a flow with higher priority are transmitted more often than packets of a flow with lower priority. These include packets of a real-time application which are preferably made as short as possible. On the other hand, packets of applications with lower priority are often considerably longer than packets with higher priority. Such a long packet prevents the transmission of other packets as long as the transmission of the packet takes, unless a method for determining the quality of service is available also in a wireless connection. This may cause considerable delays also in the transmission of packets with higher priority, and reduce the quality of service.
Problems are caused in wireless communication also by mobility of the wireless terminal device, wherein as the connection of the terminal device changes to another base station, also the Internet connection has to be connected via this base station. Thus, also the routing may have to be changed.
It is an aim of the present invention to provide a method for connecting a radio flow and a flow according to the Internet protocol in a wireless Internet connection. The method of the invention is primarily characterised in what will be presented in the characterising portion of the appended claim 1. The system of the invention is primarily characterised in what will be presented in the characterising portion of the appended claim 8. Further, the access point of the invention is primarily characterised in what will be presented in the characterising portion of the appended claim 12. The invention is based on the idea that a label is added to the packets of the data link layer in order to define which packets of the IP flow and radio flow belong to the same data flow.
The present invention gives significant advantages to the methods and systems of prior art. By providing, in accordance with the invention, IP packets with a label, it is possible e.g. to implement the access point in a more simple manner, because implementation in the network layer level is thus not required at the access point, but a structure according to the data link layer and the physical layer added with the interlayer of the invention is sufficient therein. Thus, also the transmission of packets is accelerated, because time-consuming routing in the network layer can be avoided at the access point.